“The real appeal is to put these cells into the brain in hopes of replacing those cells either killed or damaged” by radiation treatment, said UC Irvine radiation oncology professor Charles Limoli.

The researchers first irradiated the rats, then injected human neural stem cells near a brain structure called the hippocampus, where new neurons grow.

When assessed a month after the treatment, and again at four months, the rats showed significant leaps in learning and memory compared to a control group of rats.

“The data shows they are indistinguishable from controls,” Limoli said. “So it’s not an incremental gain. It’s a complete reversal, which is exciting.”

And when the rats’ brains were later examined, they revealed that about 11 percent of the surviving transplanted cells had the molecular signature of learning induced by behavior.

That showed the cells had successfully wired themselves into the rats’ memory circuits.

Some 800,000 human neural stem cells were injected into each rat, and of those that survived, 15 percent turned into neurons and 45 percent turned into supporting cells called astrocytes and oligodendrocytes.

The new findings help clear a path to human trials, although those are likely years away, Limoli said.

But it would be of enormous benefit to patients treated for brain cancer. Radiation treatment can cause severe and progressive losses in memory and learning.

“This is a real problem in kids,” Limoli said. “Kids can lose up to two to three IQ points a year. This is not only a health issue, it’s a socioeconomic burden; a lot of these kids have trouble getting jobs or contributing in the long run in society.”

Stem cells can have the capacity to turn into many types of cells in the body, driving an explosion of medical research.

The human neural stem cells used in Limoli’s study were purchased from a biotech company, and were grown from a federally approved line of embryonic stem cells.

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